Remember, all signals are analog, even those that pose as digital. Ever hear of signal integrity? Now probably not given the pedesctrian speeds you work at. You should come to DesignCon, a digital deisgn conference that's really all analog.

I suggest downloading a tone generator app, which hopefully will give you something close to a sine wave (another analog thing). I suggest checking the output on an oscilloscope set to give you at FFT (fast Fourier Transform for you digital folk). You should see the fundamental tone but you may see harmonics. Hmm maybe I can write an article comparing tone generator apps.